This specification relates to the field of night vision devices, and more particularly to an advanced image intensifier.
Image intensifiers are used in night vision devices to enhance images in low light conditions. As a general principle of operation, photons representing an image are converted into electrons, which are then substantially amplified, and finally the enhanced electron stream is again converted to photons on a phosphorescent screen, yielding a green image. There are at least four recognized “generations” of night vision technology, with the generations characterized by increasing range and clarity of images.
Up until the late 1990's image intensifiers incorporated non-gated power supply technology. The advent of gating power supplies (known in the night vision industry as “auto-gated power supplies”, referring to the fact that they incorporated feedback and control circuitry to automatically vary the duty cycle of the photocathode gating signal in response to operating levels within the image intensifier), enabled “unfilmed” image intensifier technology and improved the performance of image intensifiers in daylight conditions.
But there are problems with currently available auto-gated power supplies. The primary disadvantage is electromagnetic interference (EMI). Because of the fast rise and fall edges of the high voltage gating signal, high EMI emissions result, making it difficult and expensive to meet the requirements of military night vision EMI specifications. The EMI emissions from an image intensifier incorporating a currently-available auto-gated power supply emanate primarily from the front face of the image intensifier. This is because the high voltage gating signal that is applied to the photocathode causes it to radiate from its full active area. Because of the EMI disadvantages, night vision manufacturers have, in many cases, been prevented from achieving fast enough rise and fall times to enable gating duty cycles low enough (less than 0.001%) for full daylight operation.